“ Besides the ability to be configured for onboard diagnostics-II (OBD-II) requirements, the ME can be tuned to the emissions standards of othe markets, such as Europe and Japan. It also can be programmed for on-board refueling vapor recovery (ORVR) to allow qualifying vehicles to meet ultra-low emission vehicle (ULEV) standards.”

As new cars add more accessories, even their engine management systems become more complicated. Many late-model European cars have incorporated the Motor Electronics (ME) engine management system. Bosch control systems have been the mainstay of European engine controls for many years. Let's see why the ME system is the engine control system of choice for Mercedes-Benz, BMW and Volvo.

Besides the ability to be configured for onboard diagnostics-II (OBD-II) requirements, the ME can be tuned to the emissions standards of other markets, such as Europe and Japan. It also can be programmed for on-board refueling vapor recovery (ORVR) to allow qualifying vehicles to meet ultra-low emission vehicle (ULEV) standards.

In the past, separate control modules were often required for the specialized engine requirements of super/turbocharging, electronic throttle body control, and on-board diagnostics. ME integrates all these capabilities into a single control module, also comprising ignition control and cruise control. It interfaces with transmission and various body/chassis control modules via serial data to permit smooth engine operation with such diverse accessories as Mercedes-Benz's radar-based distronic cruise control, Porsche's tiptronic transmission control, and BMW's I-drive system.

ME's potential places it above systems like EZK/LH-Jetronic and Motronic. It controls something as seemingly simple as ignition function on Mercedes' series of three-valve, dual spark plug per cylinder 112 V-6, 113 V-8, and 137 V-12 engines. These direct ignition systems use a dual-wound ignition coil for each cylinder on the 112 and 113 engines, incorporating a single independently triggered coil circuit for each platinum-tipped spark plug. They are triggered directly from the ME control unit except in the 137 engine, which uses an energy controlled ignition (ECI) module to permit ionization-sensing knock control without the use of knock sensors. It also allows the economizing left engine bank shut-off function during part-load operation while retaining OBD-II required misfire diagnostics.

The ME control unit gives each coil multi-strike capability during extreme cold engine operation to prevent spark plug fouling with the necessarily rich mixtures. To reduce combustion chamber carbon buildup and associated hot spots that initiate preignition, the spark plugs in each cylinder are fired in alternating sequence, which prolongs spark plug life, since they run cooler. Both spark plugs are fired on every engine cycle and the time difference between the firing of the "A" plug and the "B" plug can be varied, dependent on the ignition advance map stored in the ME control unit's memory and rpm and load conditions.

Ionization-sensing knock control is not new, but it had to be refined to allow use on a super-smooth running V-12. A gasoline internal combustion engine runs most efficiently when the timing is advanced to the limit where detonation (knocking) begins. When detonation occurs in the combustion chamber, the chemistry of the burning process is altered. As any smog tech worth his dyno time can tell you, detonation increases NOx (oxides of nitrogen) in the exhaust.

The octane rating of gasoline indicates how much fuel can be compressed before it ignites spontaneously. When gas ignites by compression instead of spark from spark plugs, it causes detonation, and that is the noise you hear.

The ingenuity of the ionization-sensing process is the way it is able to measure the combustion speed without the use of expensive, power-robbing cylinder pressure sensors. Near the end of spark duration, the combustion process progresses at an expected rate. The electric potential, or to use the term loosely, resistance, of the combustion chamber gases changes as chemical ions are exchanged between molecules to change air (N2, O2) and fuel (CxHy) into exhaust gas (HC, CO, CO2, H20 and NOx).

The ion flow and the rate of combustion can be tested by sending a specified AC voltage through the spark plug via the coil from the ECI module near the end of spark duration. The actual current flow across the spark gap at this time is a measure of the ionization of the combustion gas, and the rate of reaction. By exact measurement of real-time coil current flow in the ECI module and comparison to signals stored in the ME control units memory, knock detection is performed. In addition, the ME control unit employs an adaptive learning function to compensate for age and wear of the spark plugs since the last service. Cylinder identification is performed in the ME control unit based on signals from the crankshaft and camshaft position sensors in a continuous process and timing adjusted immediately on the affected cylinder(s) to inhibit knock.

At the same time, ME retains misfire diagnostics and cylinder shut-off capability. ME can even be programmed to shut off the duty-cycled fuel pump in the event of airbag deployment to provide further fire suppression on the single line fuel system during a crash!

We certainly have come a long way since points and condensers!

© 2006 IDENTIFIX. All Rights Reserved.

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